Imaging systems, such as computed tomography (CT) scanners, are widely used for diagnostic purposes in medical and industrial applications. However, radiographic imaging of an object is complicated when the object is not stationary. The time resolution of conventional imaging systems is typically insufficient to effectively "freeze" the motion of the object. As a result, the images produced suffer from blurring effects caused by the movement of the object. Accordingly, various techniques have been developed to enable radiographic imaging of moving objects.
One such technique has focused on the pre-alignment of a gantry associated with a computed tomography (CT) scanner. The gantry is provided to synchronously rotate a radiation source and detector. Accordingly, image data can be recorded for various source and detector positions within the rotational plane of the gantry. For the pre-alignment technique to be effective, the main motion of the object must be in one direction and the gantry must rotate in a plane perpendicular to the object's motion. Therefore, the pre-alignment technique is capable of correcting for only simple motion. Accordingly, the technique is not suitable for imaging objects, such as a beating heart, which undergo complicated motions.
Another technique, which is useful for imaging an object undergoing a cyclic motion, involves the use of retrospective gating. In that technique, a continuous stream of image data is recorded but only the data collected at the desired phase of the object is utilized. Although the retrospective gating technique may collect enough projections at the same phase of the motion for reconstruction, the data acquisition time is unpredictable and the object will be subjected to a higher radiation dose than is necessary.
A third technique for imaging a moving object requires prospective gating. In the prospective gating technique, the scanner is operated in such a way that the radiation exposure and data collection occur only when the object is at the desired phase. The prospective gating technique suffers from the same uncertainty of data acquisition time as for the retrospective gating technique.
Additionally, electron beam computed tomography systems have been developed. The time resolution of these systems is generally sufficient to record images of even rapidly moving objects, such as a beating heart. However, a high capital investment, the lack of insurance reimbursement and low image quality have prevented the acceptance of electron beam CT as a routine clinical procedure.
In light of the foregoing, it would be highly beneficial to provide an apparatus and method for producing image slices of an object undergoing cyclic motion wherein the images are essentially free from blurring effects caused by the movement of the object. Additionally, the apparatus and method should enable the image slices to be constructed on-line in a quick and robust manner. Further, the apparatus and method should minimize the object's exposure to radiation.